PROJECT SUMMARY Antiviral drugs are a crucial countermeasure for influenza A virus (IAV), particularly in circumstances of increased IAV incidence or if a vaccine is unavailable (e.g., virulent H5N1 IAV). However, the emergence of IAV strains that are resistant to current antivirals1-6 (H5N1) underscores the need for new treatment strategies, particularly those that modify the host response. IAVs infect 5-20% of the US population with >200,000 hospitalizations and ~40,000 deaths annually. Morbidity and mortality are secondary to an intense systemic stress to the antiviral immune response particularly in those individuals with co-morbidities (i.e., chronic respiratory and cardiovascular diseases). Additionally, endemic IAV strains from other species (e.g., H5N1) can kill healthy individuals by a ?cytokine storm?. The emergence of pandemic strains is inevitable, as seen most recently with 2009 H1N1. Moreover, IAV?s ability to rapidly acquire increased virulence and efficient human-to- human transmission through genetic shift is a constant threat to the global population, and benign strains may rapidly evolve and cause severe morbidity and mortality. This application proposes to develop for use in patients a novel therapeutic gene knockdown strategy localized to respiratory epithelium by employing nanoplexes, an electrostatic complex of cationic polymers and anionic nucleic acids. Our preliminary findings have demonstrated that this antiviral therapy, inhibits IAV replication, decreases IAV induced lung injury and improves antibacterial host responses. This Phase I STTR application will optimize the fabrication and delivery of the nanoplexes and establish its in vitro efficacy (with respect to antiviral and IFN I stimulating activity) and toxicity. The subsequent Phase II STTR application will determine its in vivo efficacy and toxicity in mice and ferrets utilizing drug-resistant laboratory, epidemic, pandemic, and pathogenic strains.